The embodiment relates to a light-emitting device, a method of manufacturing the same, a light-emitting device package, and a lighting system.
Light-emitting devices (LEDs) include p-n junction diodes having characteristics of converting electric energy into light energy. LEDs may be formed as compound semiconductors of group III and group V elements of the periodic table, and various colors can be represented by adjusting the compositional ratio of the compound semiconductors.
When a forward voltage is applied to an LED, electrons of an n layer are combined with holes of a p layer, and thereby energy corresponding to band-gap energy between a conduction band and a valance band is released. The energy is mainly realized in the form of heat or light, and the LED emits the energy in the form of light.
For example, nitride semiconductors exhibit excellent thermal stability and wide band-gap energy, and thus have been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductors have already been commercialized and are being extensively used.
A horizontal LED is fabricated by forming a nitride semiconductor layer on a sapphire substrate and disposing two electrode layers on the nitride semiconductor layer.
A normal LED has an active structure including an InGaN quantum well and a GaN quantum barrier. Since a potential barrier is low in a boundary between the quantum well and the quantum barrier due to a difference in band-gap energy between InGaN and GaN, a carrier confinement function of injected electrons may be degraded and an electron overflow phenomenon may occur. Accordingly, the number of non-radiative carriers may increase and light-emitting efficiency may be abruptly reduced.
Meanwhile, when a current density gradually increases in an epitaxial structure in the presence of the electron overflow phenomenon, bending of a band-gap occurs. As a result, the electron overflow phenomenon may be more serious even in the InGaN quantum well having the same concentration of indium (In).
The electron overflow phenomenon generated in a quantum well having the low potential barrier may reduce the number of photons (hv) generated in a multiple quantum well (MQW) structure.
Meanwhile, the normal LED has another problem in that carrier transfer efficiency is low in the MQW structure, in addition to degradation in the electron confinement function in the quantum well.
For example, in the MQW structure, carriers additionally injected into a quantum well, which is already sufficiently filled with carriers, need to be transferred to the next quantum well. However, bending of a band-gap due to an increase in current density may cause the quantum barrier to be excessively high, which results in degradation of the carrier transfer efficiency.